Microstructure and Compressive Strength of Fly Ash/Slag Based Geopolymer Using Raman Spectroscopy

Abstract

Geopolymers are attracting attention as an environmentally friendly alternative to cement. In this study, compressive strength tests were conducted on geopolymer pastes using fly ash and blast furnace slag as active fillers. Sodium hydroxide solution and sodium silicate were used as alkaline activators. Raman spectroscopy was also employed to investigate its potential for analyzing Ca-enriched geopolymers. These results indicated that calcium aluminosilicate hydrate was formed by 7-day in the environment containing a certain amount of soluble Si in NaOH solution. This was reinforced by the formation of magnesium aluminosilicate hydrate and sodium aluminosilicate hydrate by 28-day, which may contribute to higher compressive strength. Moreover, the coexistence of high-polymerized silicates and relatively low-polymerized silicates is thought to enhance the physical entanglement of the silicates and to increase the compressive strength. These findings suggest that Raman spectroscopy is a useful tool for microstructural analysis of Ca-enriched geopolymers.